treatments/Cirsium occidentale

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Cirsium occidentale (Nuttall) Jepson Fl. W. Calif.,. 509. 1901.

Western thistle


Biennials, 5–400 cm; taproots. Stems usually 1, thinly to densely gray- or white-tomentose, sometimes ± glabrate; branches few–many, usually from above mid or near base in compact, moundlike dwarf plants, ascending to spreading. Leaves: blades oblong–elliptic to oblanceolate, 6–40 × 1.5–10+ cm, shallowly to deeply pinnatifid, lobes usually rigidly spreading, undivided or with 1–2 pairs of coarse teeth or lobes, main spines 5–15 mm, both faces gray- to white-tomentose, sometimes ± glabrate or adaxial faces green, thinly arachnoid-tomentose; basal sometimes present at flowering, petiolate or sessile and bases tapered, spiny-winged; principal cauline much reduced distally, sessile, bases decurrent or not, as spiny wings; distal much reduced, linear, ± bractlike. Heads 1–many in loose to tight clusters (barely raised above rosette in dwarf plants). Peduncles 1–30 cm. Involucres ovoid to spheric, 1.5–5 × 1.5–8 cm, arachnoid to ± loosely tomentose, often adjacent phyllaries connected by conspicuous arachnoid trichomes, sometimes glabrous or glabrate. Phyllaries in 7–10 series, subequal to strongly imbricate, green or stramineous to purple-tinged, linear to narrowly lanceolate, abaxial faces without glutinous ridge; outer and mid bodies appressed, entire, apices deflexed to spreading or ascending, short-triangular to elongate, linear-acicular, spines spreading to reflexed, 1–10+ mm; apices of inner erect, often flexuous, flat. Corollas white to lavender, pink, rose-purple, or red, 18–40 mm, tubes 8–18 mm, throats 5–7 mm, lobes 5–10 mm; style tips 4–5 mm. Cypselae ± brown, 5–6 mm, apical collars not differentiated; pappi 15–30 mm.


Varieties 7 (7 in the flora):w United States.;



1. Plants compact, rounded, moundlike; heads usually not much elevated above leaves 40c. Cirsium occidentale var. compactum
1. Plants usually erect; principal heads usually conspicuously pedunculate. (2.)
2. Corollas white to light purple or rose 40d. Cirsium occidentale var. californicum
2. Corollas deep purple to bright pink or red. (3.)
3. Plants densely white-tomentose; phyllaries persistently white-tomentose (except spines); outer phyllaries usually very long, spreading to reflexed 40g. Cirsium occidentale var. candidissimum
3. Plants variably tomentose, sometimes ± glabrate; phyllaries ± arachnoid to floccose-tomentose, sometimes green and glabrate; outer phyllaries short to long, ascending to spreading or reflexed. (4.)
4. Involucres usually about as long as wide or wider than long; phyllaries densely and persistently arachnoid with fine trichomes connecting tips of adjacent phyllaries. (5.)
5. Phyllary apices ± imbricate, the proximal usually shorter than medial and distal, lanceolate to linear-acicular, 0.5–15 mm; co- rollas bright purple 40a. Cirsium occidentalevar. occidentale
5. Phyllary apices subequal, all long- acicular, 1.5–3 cm; corollas light to deep reddish purple 40b. Cirsium occidentale var. coulteri
4. Involucres usually longer than wide; phyllaries tomentose or glabrate, sparingly or not arachnoid with fine trichomes connecting tips of adjacent phyllaries. (6.)
6. Corollas 20–24 mm, deep reddish purple; s Santa Lucia Mountains of San Luis Obispo County, California 40e. Cirsium occidentale var. lucianum
6. Corollas 23–35 mm, bright pink to red; widespread 40f. Cirsium occidentale